Semiconductor Physics · Electronic Devices and VLSI · GATE ECE

Marks 1

For non-degenerately doped n-type silicon, which one of the following plots represents the temperature ($T$) dependence of free electron concentration ($n$)?

GATE ECE 2024

The free electron concentration profile $n(x)$ in a doped semiconductor at equilibrium is shown in the figure, where the points A, B, and C mark three different positions. Which of the following statements is/are true?

GATE ECE 2024

In a semiconductor, if the Fermi energy level lies in the conduction band, then the semiconductor is known as

GATE ECE 2023

For an intrinsic semiconductor at temperature $$T=0K$$, which of the following statement is true?

GATE ECE 2023

Consider a long rectangular bar of direct bandgap p-type semiconductor. The equilibrium hole density is 10¹⁷ cm^$$-$$3 and the intrinsic carrier concentration is 10¹⁰ cm^$$-$$3. Electron and hole diffusion lengthss are 2 $$\mu$$m and 1 $$\mu$$m, respectively. The left side of the bar (x = 0) is uniformly illuminated with a laser having photon energy greater than the bandgap of the semiconductor. Excess electron-hole pairs are generated ONLY at x = 0 because of the laser. The steady state electron density at x = 0 is 10¹⁴ cm^$$-$$3 due to laser illumination. Under these conditions and ignoring electric field, the closest approximation (among the given options) of the steady state electron density at x = 2 $$\mu$$m, is _____________.

GATE ECE 2022

In a non-degenerate bulk semiconductor with electron density n = 10¹⁶ cm^$$-$$3, the value of E_C $$-$$ E_Fn = 200 meV, where E_C and E_Fn denote the bottom of the conduction band energy and electron Fermi level energy, respectively. Assume thermal voltage as 26 meV and the intrinsic carrier concentration is 10¹⁰ cm^$$-$$3. For n = 0.5 $$\times$$ 10¹⁶ cm^$$-$$3, the closest approximation of the value of (E_C $$-$$ E_Fn), among the given options is _________.

GATE ECE 2022

A bar of Gallium Arsenide (GaAs) is doped with Silicon such that the Silicon atoms occupy Gallium and Arsenic sites in the GaAs crystal. Which one of the following statement is true?

GATE ECE 2017 Set 1

A small percentage of impurity is added to an intrinsic semiconductor at 300 K. Which one of the following statements is true for the energy band diagram shown in the following figure?

GATE ECE 2016 Set 1

A piece of silicon is doped uniformly with phosphorous with a doping concentration of $$10^{16}/cm^2$$. The expected value of mobility versus doping concentration for silicon assuming full dopant ionization is shown below. The charge of an electron is $$1.6\;\times\;10^{-19}\;C$$. The conductivity (in S cm^-1) of the silicon sample at 300 K is _________________.

GATE ECE 2015 Set 2

An n–type silicon sample is uniformly illuminated with light which generates 10²⁰ electron hole pairs per cm³ per second. The minority carrier lifetime in the sample is 1 $$\mathrm\mu$$s.In the steady state, the hole concentration in the sample is approximately 10^x , where x is an integer. The value of x is __________________

GATE ECE 2015 Set 2

A silicon sample is uniformly doped with donor type impurities with a concentration of $$10^{16}/cm^3$$.The electron and hole mobilities in the sample are $$1200\;cm^2/V-s$$ and $$400\;cm^2/V-s$$ respectively. Assume complete ionization of impurities. The charge of an electron is $$1.6\;\times\;10^{-19}\;C$$.The resistivity of the sample $$\left(in\;\Omega-cm\right)$$ is _____________.

GATE ECE 2015 Set 1

In the figure ln(ρ_i) is plotted as a function of 1/T, where ρ_i the intrinsic resistivity of silicon, T is is the temperature, and the plot is almost linear.

The slope of the line can be used to estimate

GATE ECE 2014 Set 4

The cut-off wavelength (in µm) of light that can be used for intrinsic excitation of a semiconductor material of bandgap E_g= 1.1 eV is ________.

GATE ECE 2014 Set 4

A thin P-type silicon sample is uniformly illuminated with light which generates excess carriers. The recombination rate is directly proportional to

GATE ECE 2014 Set 3

At T = 300 K, the hole mobility of a semiconductor $$\mu_p\;=500\;cm^2/V-s$$ and $$\frac{kT}q\;=\;26\;mV$$.The hole diffusion constant D_p in cm²/s is__________.

GATE ECE 2014 Set 3

Drift current in the semiconductors depends upon

GATE ECE 2011

Which of the following is true?

GATE ECE 2008

Under low level injection assumption, the injected minority carrier current for an extrinsic semiconductor is essentially the

GATE ECE 2006

The concentration of minority carriers in an extrinsic semiconductor under equilibrium is:

GATE ECE 2006

The primary reason for the widespread use of Silicon in semiconductor device technology is

GATE ECE 2005

A Silicon PN junction at a temperature of 20°C has a reverse saturation current of 10 pico-Amperes (pA). The reverse saturation current at 40°C for the same bias is approximately

GATE ECE 2005

The band gap of Silicon at room temperature is:

GATE ECE 2005

The impurity commonly used for realizing the base region of a silicon n-p-n transistor is

GATE ECE 2004

n-type silicon is obtained by doping silicon with

GATE ECE 2003

The intrinsic carrier concentration of silicon sample at 300^oK is $$1.5\times10^{16}/m^3$$. If after doping, the number of majority carriers is $$5\times10^{20}/m^3$$ , minority carrier density is

GATE ECE 2002

The band gap of silicon at 300 K is

GATE ECE 2002

The units of $$\frac q{KT}$$ are

GATE ECE 1997

The probability that an electron in a metal occupies the Fermi-level at any temperature (> 0 K)

GATE ECE 1995

In a P-type silicon sample, the hole concentration is $$2.25\times10^{15}/cm^3$$. If the intrinsic carrier concentration is $$1.5\times10^{15}/cm^3$$ , the electron concentration is

GATE ECE 1995

The drift velocity of electrons in silicon

GATE ECE 1995

A p-type silicon sample has a higher conductivity compared to an n-type sample having the same dopant concentration.

GATE ECE 1994

A small concentration of minority carries is injected into a homogeneous semiconductor crystal at one point. An electric field of 10 V/cm is applied across the crystal and this moves the minority carriers a distance of 1 cm is 20 $$\mu$$ sec. The mobility (in cm²/volt-sec) will be

GATE ECE 1994

Marks 2

A non-degenerate n-type semiconductor has 5 % neutral dopant atoms. Its Fermi level is located at 0.25 eV below the conduction band ($E_C$) and the donor energy level ($E_D$) has a degeneracy of 2. Assuming the thermal voltage to be 20 mV, the difference between $E_C$ and $E_D$ (in eV, rounded off to two decimal places) is _______.

GATE ECE 2024

In an extrinsic semiconductor, the hole concentration is given to be 1.5$$n_i$$ where $$n_i$$ is the intrinsic carrier concentration of 1 $$\times$$ 10$$^{10}$$ $$cm^{-3}$$. The ratio of electron to hole mobility for equal hole and electron drift current is given as ___________ (rounded off to two decimal places).

GATE ECE 2023

In a semiconductor device, the Fermi-energy level is 0.35 eV above the valence band energy. The effective density of states in the valence band at T = 300 K is 1 $$\times$$ 10$$^{19}$$ cm$$^{-3}$$. The thermal equilibrium hole concentration in silicon at 400 K is _____________ $$\times$$ 10$$^{13}$$ cm$$^{-3}$$ (rounded off to two decimal places).

Given kT at 300 K is 0.026 eV.

GATE ECE 2023

Select the CORRECT statements regarding semiconductor devices

GATE ECE 2022

The dependence of drift velocity of electrons on electric field in a semiconductor is shown below. The semiconductor has a uniform electron concentration of n = 1x10¹⁶ $$cm^{-3}$$ and electronic charge q = 1.6x10^-19 C. If a bias of 5V is applied across a 1 $$\mu$$m region of this semiconductor, the resulting current density in this region, in kA/cm², is _________.

GATE ECE 2017 Set 1

A dc voltage of 10V is applied across an n–type silicon bar having a rectangular cross–section and a length of 1cm as shown in figure. The donor doping concentration N_D and the mobility of electrons $$\mu$$n are $$10^{16}$$ cm^-3 and 1000 cm² V^-1s^-1, respectively. The average time (in $$\mu$$s) taken by the electrons to move from one end of the bar to other end is _______________.

GATE ECE 2015 Set 2

Consider a silicon sample doped with N_D = 1×10¹⁵/cm³ donor atoms. Assume that the intrinsic carrier concentration n_i = 1.5×10¹⁰/cm³. If the sample is additionally doped with N_A = 1×10¹⁸/cm³ acceptor atoms, the approximate number of electrons/cm³ in the sample, at T=300 K, will be _________________.

GATE ECE 2014 Set 4

An N-type semiconductor having uniform doping is biased as shown in the figure.

If E_C is the lowest energy level of the conduction band, E_V is the highest energy level of the valance band and E_F is the Fermi level, which one of the following represents the energy band diagram for the biased N-type semiconductor?

GATE ECE 2014 Set 4

Assume electronic charge q = 1.6×10^-19 C, kT/q = 25 mV and electron mobility μ_n = 1000 cm²/V-s. If the concentration gradient of electrons injected into a P-type silicon sample is 1×10²¹/cm⁴, the magnitude of electron diffusion current density (in A/cm²) is _________.

GATE ECE 2014 Set 2

The silicon sample with unit cross-sectional area shown below is in thermal equilibrium. The following information is given: T=300K, electronic charge=1.6x10^-
19C, thermal voltage=26mV and electron mobility = 1350cm²/V-s